Suckling mice are known to be susceptible to oral infection with V. cholerae. Immunization of mothers with several types of vaccine permits the passive transfer of immunity to the offspring. Immunity may be either antitoxic or antibacterial. The aim of the present experiments is to determine the importance of IgA in this process. In order to assess the contribution made by this type of immunoglobulin, the MOPC plasmacytoma tumor of mice will be used to obtain pure IgA. Antibody against it, raised in rabbits, will then permit, via fluorescent labeling, an evaluation of its role in the passive immunity of baby mice. Since a variety of vaccines give good protection, it may be that more than one type of immunoglobulin is involved. We are prepared to identify the types, should this prove to develop.